Process for spinning aqueous-saline solutions of acrylonitrile polymers



A. CRESSWELL ET AL PROCESS FOR SPINNING AQUEOUS-SALINE SOLUTIONS OF ACRYLONITRILE POLYMERS Filed March 8,

INVENTORS ,4I7'HU/P (P55514424 Pa a/v44 14/. C(/MM/NGS,d/P.

- BY A-VLOKGZ r AT M- Jan. 15, 1957 PROCESS FOR PNN1NG AQUEOUl-SALINE Si)- LUHQNS 9F ACRYLGNITRELE PQLMRS Arthur Cresswell, Stamford, and Percival W. Cummings, in, Cos Cob, Coma, assignors to American Cyanamid Company, New York, N. Y., a corporation of Maine Application Marchfi, 1951, Serial No. 214,615

11 Claims. (Ci. 18-54) This invention relates to certain new and useful improvements in the art of producing synthetic fibers and other shaped structures (e. g., rods, tubes, bars, films, sheets, etc), and more particularly to the art of producing such structures from an arcylonitrile polymerization product, especially such a polymerization product which contains a major proportion (that is, more than 50%) by weight of combined acrylonitrile. Still more particularly our invention is concerned with a method of forming shaped structures from an acrylonitrile polymerization product which comprises extruding an aqueous solution of an acrylonitrile polymerization product containing a major proportion (preferably at least 85 by weight of combined acrylonitrile through a shaped orifice into a liquid coagulating bath containing from about 3% to about 25% (more particularly from about 5% to'about 20%, specifically approximately 10% by weight, of any of the water-soluble, organic or inorganic thiocyanates which yield highly hydrated ions in an aqueous solution (e. g., guanidine thiocyanate and substituted guanidine thiocyanates such as are disclosed inCresswellPatent No. 2,533,224; sodium thiocyanate and the other alkalhmetal thiocyanates; calcium, strontium, barium, zinc, tin, lead and other water-soluble metallic thiccyanates; etc.) The acrylonitrile polymerization product is dissolved in a concentrated aqueous solution of the sarncwater-soluble thiocyanate which is a component of theaforementioned liquid coagulating bath, which bath, in all cases, is at a-temperature not exceeding +10 C., advantageously not exceeding +5- C. and preferably below -'C., or at about 0 C. in some cases, e. g-., from about C. to. 0 C.

The stretchable, gelled fiber or other shaped structure whiehis precipitated in the aforesaid liquid coagulating bath is then preferably washed by any suitable means until it is substantially free from thiocyanate. The washed, shaped structure, e. g., in fiber form, is then stretched in the presence of moisture and at a temperature within the range of about 70 C. to about 110C.

Various methods of producing filaments, films and other shaped articles from polymeric acrylonitrile (homopolymeric acrylonitrile) and from copolymers or interpolymers of a major proportion of acrylonitrile and a minor proportion of another monomer or monomers heretofore have been suggested. For example, in .Rein U. S. Patent No. 2,117,210 it is proposed that polyacrylonitrile be dissolved in a quaternary ammonium compound such as benzyl pyridiniurn chloride,

and that the resulting solution be employed in making films threads and other shaped bodies therefrom. Also, .in Rein U. S. Patent No.

2,140,921 it is proposed that various polyvinyl compounds including polyacrylonitrile and eopolymers of acrylonitrile with another vinyl compound be dissolved in concentrated aqueous solutions of inorganic (metallic) salts, e. g., the chlorides, bromides, iodides, thiocyanates, perchlorates and nitrates, and that the resulting solutions be used in the manufacture of threads, films, etc. Various organic solvent solutions of polyacrylonitrile and copolymersof at least 85% by weight ofacr-ylonitrileiwith another-monoited States Patent 0 mer are disclosed in U. S. Patents 2,404,713-72-8, and also the use of such solutions in formingfilms, filaments, etc., therefrom. In most of these latterpatents the aforementioned Rein patents are referred to, as well as the difficulties encountered when effort was made to produce'useful filaments and other shaped articles from polyacrylonitrile solutions of the kindproposed by Rein.

The invention disclosed and claimed in the copending application of one of us (Arthur Cresswell), Serial No. 772,200, filed September 4,1947, now Patent No. 2,558,- 730, dated July 3, 1951, is based on the discovery that useful films, filaments, threads and other shaped articles can be produced fromacrylonitrile polymerizationprodnets of the kind describedtherein and in the aforementioned patents, as well as hereinafter, byprecipitating or coagulating the polymerization product in approximately its desired shape from a water-coagulable solution thereof, more particularlya concentrated aqueous salt solution of the kind disclosed by Rein in his Patent No. 2,140,- 921, the precipitation being. effected by contacting the said solution with a cold aqueous coagulant, more particularly water alone, at a temperature not substantially exceeding +10 C. This coagulant is a non-solvent for the polymerize -'on product but will dissolve the solvent in which the said product is dissolved. Surprisingly it was found thatby keeping the temperature of the aqueous c0- agulatingibath at or below 10 C., e. g., within the range of'l5' C. to +10" C. and preferably at from about C. to about +'5 C., the precipitated gels in general are clear or substantially clear, tough, ductile and, in filament, thread, or other form, can be stretched to orient the molecules, therebyincreasing the cohesiveness, tensile strength, toughness, resilience..,and otherwise improving the properties of the finished product. In marked contrast, if temperatures materially above +10 C. be employed, e. g., temperatures of the order of to C. or higher, the precipitated gels in general are hazy or opaque, weak, friable, have little or no toughness or duetility and are notadapted for stretching to orient the molecules andthereby' improve the properties of'the dried material.

The present invention-is an improvement upon the invention disclosedand' claimed in the aforementioned copending Cresswellapplication Serial No. 772,200, and involves the use of a new and novel'low-temperature liquid coagulating-bath in anew and improved method of pro: ducing shaped articles, e. g., fibers, films, etc., from an acrylonitrile polymerization product dissolved in a concentrated aqueous solution of a water-soluble thiocyanate which yields highly hydrated ions inan aqueous solution, e. g., sodium or calcium thiocyanate, etc.

It is an object of the present invention to-provide a coagulating bath and spinning process whereby the recovery of the solvent used in dissolving the acrylonitrile poly merization product will bemore economical by reason of the fact that there'will beless water to evaporate in producing a concentrated aqueous solution suitable for reuse as a solvent for the pol'ymericor copolymeric'acrylonitrile.

Another object of the invention is to provide a more economical process, specificall'y'by decreasing the amount of refrigeration required for cooling the liquid coagulant, since there is no make-up water that has to be refrigerated as is the case when water alone is used as the aqueous coagulant and'a bathtemperature of, ,for example, +0.5" C. Still another object ofthe invention isto provide a new and novel liquid coagulating bath which can be effectively and economically used in a wet-spinning; process. and whereby bath temperatures below-0 .C. canhereadily .obtained and maintainedduringthe .spinningoperation.

Other objects. of the invention will. be apparentto those 7 v a skilled in the art as the description of the invention proceeds.

The foregoing and other objects are attained by practicing the invention hereinafter described.

The novel features which are characteristic of our invention are set forth in the appended claims. The invention itself, however, will best be understood by reference to the following more detailed description when considered in connection with the accompanying drawing in which the single figure is a diagrammatic view of one form of apparatus that may be used in practicing the invention and which is illustrative thereof.

Polymeric acrylonitrile and acrylonitrile copolymers containing a major proportion by weight of combined acrylonitrile, preferably those containing in the molecules thereof an average of at least about 85% by Weight of combined acrylonitrile, are used in practicing the present invention. These acrylonitrile polymerization products are prepared by methods well known to those skilled in the art. The polymeric and copolymeric acrylonitriles which are used in carrying our invention into effect may be of any suitable molecular weight, but ordinarily the .molecular weight (average molecular weight) is within the range of 15,000 to 300,000 (more particularly from 35,000 to 300,000) or higher, and advantageously is within the range of about 50,000 to about 150,000, as calculated from viscosity measurements using the Staudinger equation (reference: U. S. Patent No. 2,404,713). The expression acrylonitrile polymerization product containing a major proportion by Weight of combined acryionitn'le as used herein and in the appended claims, means a polymerization product (polymen copolymer or interpolymer or mixture thereof) containing in its molecules a major or preponderant proportion (more than 50%) by weight, specifically an average of at least about 85% .by weight of the acrylonitrile unit, which is considered to be present in the individual polymer molecule as the group or, otherwise stated, a major proportion, more particularly at least about 85%, by weight, of the reactant substance converted into and forming the polymerization product is acrylonitrile (combined acrylonitrile).

Illustrative examples of monomers which can be ccpolymerized or interpolymerized with acrylonitrile to yield a polymerization, product (copolymer or interpolymer) containing in the polymer molecules a major proportion by Weight of combined acrylonitrile are compounds containing a single CH2=C grouping, for instance the vinyl esters and especially the vinyl esters of saturated aliphatic monocarboxylic acids, e. g., vinyl acetate, vinyl propionate, vinyl butyrate, etc.; vinyl and vinylidene halides, e. g., the vinyl and vinylidene chlorides and fluorides; allyl-type alcohols, e. g., allyl alcohol, methallyl alcohol and other unsaturated monohydric alcohols; allyl, methallyl' and other unsaturated monohydric alcohol esters of monobasic acids, e. g., allyland methallyl acetates, laurates, cyanides, etc.; acrylic and alacrylic acids (e. g., methacrylic, ethacrylic, etc.) and esters and amides of such acids (e. g., methyl, ethyl, propyl, butyl, etc., acrylates and methacrylates, acrylamide, methacrylamide, N-methyl, -ethyl, -propyl, -butyl, etc., acrylamides and methacrylamides, etc.); methacrylonitrile, ethacrylonitrile and other hydrocarbon-substituted acrylonitriles; unsaturated aliphatic hydrocarbons containing a single CH2=C grouping,

e. g., isobutylene, etc.; and numerous other vinyl, acrylic and other compounds containing a single CH2=C group-.

ing which are copolymerizable with acrylonitrile to yield thermoplastic copolymers. Alkyl esters of alpha, beta unsaturated polycarboxylic acids also can be copolymerized with acrylonitrile to form copolymers which can be used in practicing the present invention. Examples of such esters are the dimethyl, -ethyl, -propyl, -butyl, etc., esters of maleic, fumaric, citraconic, etc., acids,

The spinning solution is prepared by dissolving polymeric or copolymeric acrylonitrile in a concentrated aqueous solution of a water-soluble, organic or inorganic thiocyanate which yields highly hydrated ions in aqueous solution and which, mainly to simplify the recovery problem, is of the same kind used in the aqueous coagulating bath. Numerous examples of such salts have been given in the first paragraph of this specification. The concentration of the water-soluble thiocyanate in the water in all cases is sufliciently high so that the resulting solution will dissolve the acrylonitrile polymerization product. The concentration of thiocyanate in most cases is substantially above 40% (e. g., from 45-50% to -60%) of the total Weight of the solution of thiocyanate dissolved in water, the upper limit being a saturated solution of the thiocyanate in water.

With reference to the drawing, a thiocyanate solution of polymeric or copolymeric acrylenitrile of the kind just described, which solution has been filtered (if necessary) and deaerated, is passed under pressure from a supply reservoir (not shown) through the conduit 10 into a spinneret coupling or heading 12, which preferably is designed so that the solution can be heated, e. g., by electrical or other means prior to extrusion through the spinneret 14. A suitable design of a spinneret coupling, which is heated by electrical means, is shown in Fig. 2 of the drawing accompanying the copending application of Arthur Cresswell, Serial No. 772,200, filed September 4, 1947. This spinneret assembly is broadly and specifically claimed in Cresswells application Serial No. 205,- 778, filed .Tanuary 12, 1951, as a division of the said application Serial No. 772,200 and now abandoned. Another suitable design of a spinneret assembly including a spinneret coupling provided with means for heating the spinning solution immediately prior to extrusion is disclosed and claimed in the copending application of Arthur Cresswell, Serial No. 201,823, filed December 20, 1950 and now abandoned.

The spinneret assembly illustrated in the drawing accompanying the present application is of the electrically heated kind such as is shown in Fig. 2 of the aforementioned Cresswell application Serial No. 772,200. The device comprises a male coupling 16 in which is annularly spaced an electrically heated cartridge provided with leadin wires 18. This cartridge advantageously may be fitted in the male coupling 16 by means of a liquid-tight plug. The electrically heated cartridge is so positioned as to project beyond the lower end of the male coupling 16 and close to, or actually into, the cup of the spinneret .14, which is attached by female coupling 20. The solution being charged through the conduit 10 passes'annularly between the outer wall of the cartridge and the inner wall of the male coupling 16 and thence through 7 at the point of extrusion, better operating conditions are attained since the higher temperature of the spinning solution facilitates the removal of the resulting waterswollen or gelled filaments from the face of the spinneret at a greater speed when other conditions are the same.

In this Way, the amount of fiber or yarn that can h produced from a particular unit is increased The spinneret coupling 12 may be held by any suitable means (not shown) above the liquid coagulating or precipitating bath 22 in vessel 24. The coupling prefer- --ahly-'-is positioned so =that -only the face of-the spinneret eorrtacts-the co'agulating bath.

l he bath 22 comprises anaqueous solution containing from about 3 to about 25% by weight, of a .water- -solublethiocyanate which yields highly hydrated ions in i an aqueous solution. Numerous --examples of such thiocyana-tes have been given hereinbefore. ":We prefer-to use an aqueous solution containing from about-3% .to about 255%, by weight, of eithersodium thiacyanate: or calcium .ihiocyana-te. From apractical-standpoint-and to simplify :the recoveryiprobiem, it is-desirablezthat'the thiocyanate ;employed inproducing the liquidcoagulatingi-bath be of thesarneikind as that used'in forming the concentrated aqueous solution in which the acrylonitrile :polymeriza- ;tion product is dissolved.

As the spinning solution is forced under pressure through the openings in the :spinneret 14, it coagnla-tes or precipitates in the f-forruof solid, water-swollen or gelled filamentsiZ upon enteringzthecoagulating bath22 which is maintained at a temperature not exceeding +.l C.-by any-suiatblemeans, and-prefcrablyismaintained at or below 0C., e. g., at 9 C. to 0.5 ,C. Byusing such a coagulating bath, coagulation takes place somewhat more gradually than when cold'water alone is used us the liquid coagulant, other conditions being the-same, thereby minimizing or obviating the formationof a dense skin on the surfacelof the individual filaments upon subsequent drying, .withobvious disadvantages from the standpoint of ease of dyeing, etc.

The thiocyanate solution comprising the bath 22 may be refrigerated or cooled to the desired low temperature and circulated through the vessel 24, being introjduced through the conduit 28 and withdrawn through the-conduit 3d. The maximum temperatureof-thecoagulating .bath.22.iscritical, since,at temperatures-materially above 1 ;C., the resultingrgel-led fiber does nothavewsuf- =ficient toughnessand ductility so. that the fiberacanibe stretched adequately vin order to orient ,the emoleeules along the fiber axis. Reference is made to-the aforementioned Cresswell cop ending application SerialNoJ 72,200, .for a more complete discussion on the -matter-of im- .jportancecf the temperature of acoagulating bath'when -producing .a synthetic fiberfrom a spinning solution :of .the kind vused inpracticing the present -invention.

Ihe coagulated.fiber-in gelled,state is led-,through bath ,22, which preferablyis of the circulating type by any suitable means. The geliedfiber- -may bo led ihfOllgllzihB bath.2,2, merely with the aid ofa:guide or-sheaue 32 11315 .shownin theaccompanyin-g drawing. 'l"-he;gelled';fiber .26 is then preferably was'hetl-byqany suit-able'rneanstuntil .it is .substantiallyfree from thiocyanate. Thusthe-fiber .may be washed using equipment such as is SllOWHbYTWEY ofillustration in the drawing. Asthereshown-thefiber 126 after leaving the liquid coagulating batht22 ;passes over,t-he.revolving wheel or godet 34-into;-the-.wash water t .36 containing in vessel 38 and-:thence-overthe guide irollor .sheave:40. The-wash water36 is-introduced into the-vessel '38 through the conduit .42 and -fiows-out of this vessel through the conduit 44. The wash water maybe at any suitable temperature ranging, forexample, from slightly above 0-C..to 01 C. :Incertain cases, for instancewhen a solution containing a lOWzCOD- tcentrationte. g 315%,) .ofthiocyanate isusedeandithe .coagulated fiber is retained :in this solution ;-f.0r :a :relatively'long period, then the wash watc -may be athigher --temperatures oftheorder 0f or- Qor more.

If the wash .water is to be cooled,.this may be done 'oy', circulating refrigerated water through the vessel :33, iorrthe vessel 38 maybe provided-with,suitable;cooling .Coils whereby the water contained in, or circulating flII'DHghfthSiVESSBlfl/Vlll. hemaintained atsthe desired low temperature. Ordinarily, :water at from.0.5':C. toroom temperature (2 -1-30 C.) can benlsed lSfltlSfaCtOPlllylltD wash-the gelle'd fiber. A preferredamethod ofwashing 'mixerto 9 C. -.with nitrogen,; and '6.25 kg. of moist (34.5% water) acrylonitrile-rnethyl'acrylate copolymer -was added to the on at slow speedier 24 hours at room temperature. result-ing solution of copolymer was then filtered in a fiber i is z. adtganced "in a' helicale-path fitter tithe tr lls 1 Whi upplying a-a .ietwr jets-10f .cwater :to gthe gadv-ancing fiber. Such a method of washing-is disclosed, .forinstance, in thecopending application;of Arthur Cresswell, Serial No. 73,078; filecllanuaryf27, 1949,2110W :Batent No. 2,558,731, dated:luly -3, 21951, as well-.as in the copending applica- .1101! aof Arithur tcresswelltandlrvin Wizon, Serial No. 07,786, :filed June 8, 1949, now --Patent No. 2,558,733,

fiatedflulyi 3, 1951.

' With-further reference to the drawing, the washed fiber lfiafter lea'ting the'bath of-wash water :36 passes over the revolving.wheeltor godet '48 and the auxiliary roller "50,-b-eing wrapped one-or-more (e. g., two orthree) times-about each, through-the hot, aqueous, liquid medium 52,:e. g., hot-water, contained'in the stretch trough -54, and thence over the godet 56 and-the auxiliary roller 58, about each of which the:fiber:also is wrappedone or more (e. g, two or three) times. .ThegodetS iscaused to revolve at aperipheral. speedgreater thanthat ofthe godet 48; in other words, the surface speed of the godet 56 is suchthatthe ratio of speeds ofgodets 48 and 56 isyproportional to the. desired stretch which is to be applied to the fiber as'itpasses through thehot, aqueous, liquidmediumdfi, which enters the stretch trough54 through the conduit ll and leaves through the conduits '62. A type of stretch trough which is suitable for use is disclosed and'clairned in the copending application of Arthur Cresswell, Serial No. 146,880, filed February 28, 11950, nowPatent No. 2,558,734, dated July 3, 1951.

After leaving the godet56 thestretched or oriented gelled fiber64 canbe collected with other fibers produced i'fromcther spinning ,units'into theform of a tow, which wthereafiter is cut into sta'ple'fiber length and subsequently processed to yield a crimped staple fiber, for instance as described in the ,copending application of Arthur Cresswell,"Se1ialNo. 875592, filed 'April' 15, 1949, nowiPatent No. 2,558,732, datedJuly 3, 1951, or by other suitable means. When a continuous "filament yarn is to be pro- ,duced, the subsequent.processing operations preferably :are carried out as described, for example,-in.the aforementioned copending applicationv of Arthur Cress-well and Irvin -Wizon, Serial No. 97,786.

.In order .that those skilled in the art may better-understand how the present invention can becarn'ed into effect, the following examples are givenby way of illustration and not by way of limitation. Allpartsandpen centages are. by :weight.

Example 1 his.- example illustrates the use of a liquid coagulating bath comprising an aqueoussolution containing approximately 10% of sodium thiocyanate.

-A: .oluti1on of36.42-kg. of 55.9% aqueous sodium thio- ;cyanate and ,2.06-.-lcg. of water-was cooled in.a turbo- The air above the solution was displaced solution over a period of 1-minute by means of a Syntron feeder while the solution was stirred rapidly. (The copolymer was produced bypolymerization in an aqueous solution of a mixture-of- %-,acrylonitrile-and-5% methtyl .acrylate. The kinematic viscosity ofa solution of 1 gram of the dry copolymer in ml. of 60% aqueous sodium thiocyanate solution -.was 21.4 centipoises, which corresponds to an average molecular weight for the co- ;polymer of approximately 75,0002) After all of the copolymer had' been added, the mixer was again-flushed with nitrogen and re-sealed. The mixing was carried The plate-and-frame press at a flow rateof 1.09 gallonsper square foot per'hour. The filtered solution was stored under-vacuum until lm-bble-free. The solution contained 4827 .70 sodium thioc'y-anate -'-and 9:1-6% -copolymer. its

the g'elledfiber -is on-eonverging washrolls whereby-the Y75 visc'osity, :as determined by measurin'g xthe time for a Monel ball, /s inch in diameter and weighing 0.142 gram, to fall through a 20-cm. column of the solutionmainspinning solution was heated in a spinneret assembly im-' mediately prior to extrusion to about 75-80 C. by means or" a heated portion within the assembly. The gelled filaments were led downwardly 4 inches to a submerged roller and then back to the surface of the coagulating bath, after which the unstretched, gelled thread was washed until substantially free from sodium thiocyanate. More particularly, washing was effected by leading the gelled thread to a pair of inclined wash rolls which converged slightly toward each other so that the thread would advance in a helical path from the feed-on end to the take-E end. On these wash rolls 37 feet of gelled thread in the form of advancing helices could be stored. As the helices advanced along the rolls, the

thread was washed with water cooled to about 0 C. The V washed, gelled thread was stretched 852% in water heated to 99 C., after which it was treated with a 2% solution of the diguanidinium salt of octadecylsulfosuccinate as an antistatic finish. After this treatment, the thread was continuously dried, heat-retracted 8.1% by passing it, while relaxed and free to contract linearly, through a slot heated to about 550 F., and then ringtwisted at a speed of 6466 meters per minute. The properties of 78.5 denier yarn spun in this manner were as follows: tenacity, in grams per denier, 4.83 dry, 4.71 wet, 2.47 loop and 2.48 knot; elongation, 13% dry and 13.5% wet.

Example 2 This example illustrates the use of a liquid coagulating bath comprising an aqueous solution containing approximately 10% of calcium thiocyanate.

A solution of 36.40 kg. of 55.9% aqueous calcium thiocyanate and 3.72 kg. of water was cooled in a turbomixer to 3 C. The air above the solution was displaced with nitrogen, and 4.88 kg. of moist acrylonitrile-methyl acrylate copolymer of the kind described under Example 1 was added to the solution, dissolved, filtered and stored in the same manner described in that example. The solution contained 48.5% calcium thiocyanate and 7.38% copolymer. its viscosity, determined as described under Example 1, was 18.8 seconds.

The above solution was spun into a fiber in essentially the same manner set forth under the preceding example i with the exception that the solution was continuously extruded through the spinneret into a coagulating bath comprising an aqueoussolution containing approximately 10% of calcium thiocyanate, the washed,.gelled thread was stretched 855% in 99 C. water, and the percent to This example illustrates the use of a liquid coagulating bath comprising an aqueous solution containing approximately 26% of calcium thiocyanate.

A solution of 41.5 kg. of 54.5% aqueous calcium thiocyanate and 1 kg. of water was cooled in a turbo-mixer to 10 C. The air above the solution was displaced with nitrogen, and 7.5 kg. of moist (53.3% water) acrylonitrile-methyl acrylate copolymer of the kind described under Example 1 was added tothe solution over a period of 1 minute by means of a Syntron feeder while the soluwas dried continuously.

tion was stirred rapidly. The mixer was again flushed with nitrogen and re-sealed. The mixing was carried on at slow speed for 16 hours at 45 C. The resulting solution of copolymer was then filtered'at 45 C. in a plate-and-frame press. under vacuum until bubble-free. copolymer, and its viscosity (determined as described under Example 1) was 23.4 seconds.

The above solution was spun into a fiber in essentially the same manner described under Example 1 with the following exceptions: A 40-hole spinneret having holes 120 microns in diameter was used, and the solution was continuously extruded through the spinneret into a coagulating bath comprising an aqueous solution containing approximately 20% of calcium thiocyanate. Also, the washed, gelled thread was stretched 600% in 99" C. waten'and the continuously dried thread was heat-retracted 11% by passing it, while relaxed and free to contract linearly, through a slot heated to about 700 F.

The properties of 114 denier yarn spun in this manner were as follows: tenacity, in grams per denier, 3.29 dry, 3.38 wet, 2.04 loop and 2.06 knot; elongation, 14% dry and 16% wet. As in the previous examples, the heattreated yarn was led directly from a relaxation godet to ring twister for twisting and continuous collection (in this case at 16 meters per minute) on a take-up spool or bobbin. in this particular example there was inserted approximately 10.0 turns per inch 5 twist into the yarn as it was being continuously collected.

Exmnple 4 This example illustrates the use of a liquid coagulating bath comprising an aqueous solution containing 3 to 5% of calcium thiocyanate.

A solution of 6.2 kg. of 54.6% aqueous calcium thiocyanate and 198 g. of water was adjusted to a pH of 6.2. A slurry of 525 g. of dry acrylonitrile-methyl acrylate copolymer in 775 g. of water was added to this aqueous calcium thiocyanate solution with cooling. (The copolymer was produced by polymerization in an aqueous soluton of a mixture of acrylonitrile and 5% methyl acrylate. The kinematic viscosity of a solution of 1 gram of the dry copolymer in ml. of 60% aqueous sodium thiocyanate solution was 23.6 centipoises, which corresponds to an average molecular Weight for the copolymer of approximately 83,000.) The batch was mixed for about 16' hours at room temperature, after which it was heated to 45 C. and filtered at that temperature in a plate-and-frame press. The filtered solution was stored under vacuum until bubble-free. Analysis of the solution after standing 11 days at room temperature showed that itcontained 7.12% of copolymer, and its viscosity (determined as described under Example 1) was 27.6 seconds.

The above solution was spun into a fiber continuously by extruding it through a 40-hole spinneret with holes of 200 microns diameter into an aqueous coagulating bath consisting of an aqueous solution containing from 3 to 5% of calcium thiocyanate. The coagulating bath was cooled to and maintained at a temperature of between about 1 C. and about 0.5 C. The spinning solution was heated immediately prior to extrusion as described under Example 1. The coagulated fiber was carried back and forth through the bath at 2.24 meters per minute by means of a power-driven submerged godet positioned at one end of the bath and a set of free-running rollers at the other end. The total bath travel of the gelled fiber or thread was about inches. The spun fiber was led out of the coagulating bath over guide rollers and a driven godet A through a trough containing water heated to about 99 C. The fiber was stretched 880% in this hot water by leading it over a second driven godet B, the peripheral speed of which was greater than that of the godet A. After applying a liquid composition containing an antistatic agent, the stretched fiber The dried thread was heat-re- The filtered solution was stored It contained 6.55% of jira'cted'9' by passing it, while relaxed andf'reel'tocontact linearly,"through a slot'heat e'd to 'abtmtr'SSO F., and was then "ring-twisted at 17.6 meters'per'minute. ""I'hegprop- 'e'rti'es of 92 denier yarn spun inthismanner were asifollows: tenacity, in grams 'per denier, 3";72 dry'and 3180 war; dry elongation, 16%.

Example 5 This example illustrates theu'se of -a liquid "coagulating bath comprising an aqueous solution -containing 25% of calcium thiocyanate.

A solution of 5896 g. of 545% aqueous calcium thiocyanatesolutionwasdiluted with- 6-14-g. (if-water; arid -'the resulting solution was adjusted to a pH of 7.0"with hydrochloric acid. Four hundredandfive ('405) 'grams of 'dry acrylonitrile-methylacrylate copolymer' was dissolved in 5380 g. of the above-calcium thiocyanate solu- "tion. (The copolymer was produced by polymerization in an aqueous solution of a mixture of 9 5% acrylonitrile and-5% methyl acrylate. The-kinematic viscosity :of a solution of 1 gram of the dry copolyrn'eriin 100 mlsof 60% aqueous sodium thiocyanate 1 solution was 30.1 centipoises.) After filtration and deaeration,.- analysiscof the solution showed that it contained 6.77% of copolymer. Its viscosity, determined asdes'cribed under Example l, was 87.2 seconds.

The above solution was extruded through .a 40-hole spinner'et, having openings 90 micronsin diameter, into a 25% aqueous solution offcal'cium'thiocyana'temain- 'tained at a'temperature of about 4C. The solution was extruded at a rate'of 3384 cm. per minute. '-A complete bundle of 'filaments'was readilycollected and pulled away from the'face'of the spinneret'at a speed'of'"6.75 meters per'minute. 'Thebundle'was readily Washed-with water to remove the excess thiocyanate.

Example 6 This example illustrates the results obtained when elfort is made to use a liquid coagulating bath comprising an aqueous solution containing a water-soluble thiocyanate in a concentration substantially above 25%, more particularly 30% and 40% solutions of calcium thiocyanate.

The spinning solution employed in this example was the same as that used in Example 5. When this solution was extruded through a 40-hole spinneret having openings 90 microns in diameter, into a tion of calcium thiocyanate maintained at about 4 C., coagulation was so slow that a complete bundle of filaments could not be picked up, showing that the use of an aqueous coagulating bath containing 30% of calcium thiocyanate is not practical or feasible. When the same solution was similarly extruded into a 40% aqueous solution of calcium thiocyanate maintained at about 4 C., no coagulation whatsoever occurred.

It will be understood, of course, by those skilled in the art that our invention is not limited to the specific coagulating baths disclosed in the above illustrative examples. Thus, instead of using a liquid coagulating bath comprising an aqueous solution of sodium or calcium thiocyanate in a concentration of from about 3% to about 25%, by weight, we may use concentrated aqueous solutions of any other water-soluble thiocyanate in the aforementioned proportions. Numerous examples of watersoluble thiocyanates have been given hereinbefore.

Likewise, it will be understood by those skilled in the art that our invention is not limited to the specific polymerization product, namely, a copolymer of acrylonitrile and methyl acrylate, which is given in the illustrative examples. Thus, instead of this particular copolymer, we may use homopolymeric acrylonitrile or any other copolymer, more particularly a thermoplastic copolymer, of a major proportion of acrylonitrile and a minor proportion of another monomer or monomers, numerous examples of which latter also have been given hereinbefore. Furthermore, we are not limited to the partic ular proportions of copolymerizable monomers given in 30% aqueous soluwater alone-isnsed as' 'the aqueous "temperaturebt for example,- +0.5 1C. By thus-decreasing "the amount or refrigeration-required,' the process is the "examples. :"For instance, instead of using .acryloni ttril'e' an'dmethyltacrylate'in a'w'eight ratio'of95'% of"the 'former to""5% or the latter ituformingthebopolyme'ror interpolymer we rnay use the'se-andother copolymei'izable ingredients -incluc'iing aciylonitrile in various other proportions, 'e.; g., in a-weigh'tra'tio of from about-551% to about 99% of acrylonitrile-to from about-45% to -about 1% of' methyl aerylate, -acrylan1ide, or otherco'pt'i'lyii'nerizable monomer or monomers, *more particularly from, by weight, about to-aboiit ot=acrylonit1=ile--'to from about 15% to about 5'%-=of methyl acr'ylate or other copolymeiizable monomer-or r'nonomers.

The'pre'se'nt invention provides numerous practical advantages, :especially as compared with the use; of water alone asa-liquid coagulating bath. Specifically, themecovery' of -the solvent used in diss'olving the acrylonitrile polymerization product i's'inore economical :byzreasonuof the iactthat thereis'less water to evaporatein'producing a concentrated aqueous solution suitable -tor re=use' as a solvent for the polymeric orzcopolymeric acrylonitrile. Another outstandingadvantage-results from the'tact'that "the amount'of-refrigeration required for cooling the. liquid coagulantism'aterially decreased,- since there is no makeup water thathas 'to be refrigerated as :is-the 'caseiwhen coagulant: and a bath made more economical.

Another advantage "flowing fact that the 'thiocyanate reduces coagulating .bathand, therefore,-

:from the .invention is. the thezfreezing point ofthe makes possiblefthe use of lower :temperatures than -:can;'be obtained-with water alone. Still. .anothen valuable. and 'unobvious .advantage of the invention is that the use of our coagulating bath results in a somewhat more gradual precipitation or coagulation of the spinning solution than is possible with cold water alone (other conditions being the same), and thus minimizes or obviates the formation of a dense surface layer when the gelled fiber subsequently is dried. Shlch a dense surface layer has obvious disadvantages from the standpoint of ease of dyeability and lack of uniformity in the structure of the fiber.

The term fiber as used generically herein and in the appended claims is intended to include within its meaning both monofilaments and multifilaments.

We claim:

1. A method of forming shaped structures from an acrylonitrile polymerization product which comprises extruding an aqueous solution of an acrylonitrile polymerization product containing a major proportion by weight of combined acrylonitrile through a shaped orifice into a liquid coagulating bath comprising an aqueous solution containing from about 3% to about 25%, by weight, of a water-soluble thiocyanate which yields highly hydrated ions in an aqueous solution, said coagulating bath being at a temperature not exceeding +10 C. and said acrylonitrile polymerization product being dissolved in a concentrated aqueous solution oi the same water-soluble thiocyanate which is a component of the said liquid coagulating bath.

2. A method as in claim 1 wherein the acrylonitrile polymerization product contains at least 85% by weight of combined acrylonitrile.

3. A method as in claim 1 wherein the water-soluble thiocyanate is sodium thiocyanate.

4. A method as in claim 1 wherein the water-soluble thiocyanate is calcium thiocyanate.

5. A method as in claim 1 wherein the liquid coagulating bath is at a temperature not exceeding about 0 C.

6. A method as in claim 1 wherein the liquid coagulating bath comprises an aqueous solution containing from about 5% to about 20%, by weight, of a water-soluble thiocyanate which yields highly hydrated ions in an aqueous solution.

, awry 7. A method of producing synthetic fibers from an acrylonitrile polymerization product which comprises extruding an aqueous solution of an acrylonitrile polymerization product containing a major proportion by weight of combined acrylonitrile through a shaped orifice I into a liquid coagulating bath comprising an aqueous solution containing from about 5% to about 20%, by weight, of a water-soluble thiocyanate which yields highly hydrated ions in an aqueous solution, said coagulating bath being at a temperature not exceeding about C. and said acrylonitrile polymerization product being dissolved in a concentrated aqueous solution of the same water-soluble thiocyanate which is a component of the said liquid coagulating bath; and washing the stretchable, gelled fiber which is precipitated in the said liquid coagulating bath.

8. A method of producingsynthetic fibers from an acrylonitrile polymerization product which comprises extruding an' aqueous solution of an acrylonitrile polymerization product containing at least 85% by weight of combined acrylonitrile through a shaped orifice into a liquid coagulating bath comprising an aqueous solution containing from about to about 20%, by weight, of a watersoluble thiocyanate which yields highly hydrated ions in an aqueous solution, said coagulating bath being at a temperature below 0 C. and said acrylonitrile polymerization product being dissolved in a concentrated aqueous solution of the same water-soluble thiocyanate which is a component of the said liquid coagulating'bath; washing the stretchable, gelled fiber which is precipitated in the said liquid coagulating bath until'it is substantially free from thiocyanate; and stretching the washed, gelled fiber in the presence of moisture and at a temperature within the range of about 70 C. to about 110 C.

9. A method as in claim 8 wherein the liquid coagua liquid coagulating bath comprising an aqueous solution containing from about 5% to about 20%, by Weight, of a water-soluble thiocyanate which yields highly hydrated ions in an aqueous solution, said coagulating bath being at a temperature of from about 0 C. to not exceeding +10 C. and said acrylonitrile polymerization product being dissolved in a concentrated aqueous solution of the same water-soluble thiocyanate which is a component of the said liquid coagulating bath; washing the stretchable, gelled fiber which is precipitated in the said liquid coagulating bath; and stretching the washed, gelled fiber in the presence of moisture and at a temperature within the range of about C. to about C.

11. A method as in claim 10 wherein the water-soluble I thiocyanate is sodium thiocyanate.

References Cited in the file of this patent UNITED STATES PATENTS 1,465,994 Palmer et al. Aug. 28, 1923 2,004,271 Dreyfus June 11, 1935 2,025,730 Dickie et al. Dec. 31, 1935 2,140,921 Rein Dec. 20, 1938 2,420,565 Rugeley et al May 13, 1947 2,558,730 Cresswell July 3, 1951 2,558,731 Cresswell July 3, 1951 

1. A METHOD OF FORMING SHAPED STRUCTURES FROM AN ACRYLONITRILE POLYMERIZATION PRODUCT WHICH COMPRISES EXTRUDING AN AQUEOUS SOLUTION OF AN ACRYLONITRILE POLYMERIZATION PRODUCT CONTAINING A MAJOR PROPORTION BY WEIGHT OF COMBINED ACRYLONITRILE THROUGH A SHAPED ORIFICE INTO A LIQUID COAGULATING BATH COMPRISING AN AQUEOUS SOLUTION CONTAINING FROM ABOUT 3% TO ABOUT 25%, BY WEIGHT, OF A WATER-SOLUBLE THIOCYANATE WHICH YEILDS HIGHLY HYDRATED IONS IN AN AQUEOUS SOLUTION, SAID COAGULATING BATH BEING AT A TEMPERTURE NOT EXCEEDING +10*C. AND SAID ACRYLONITRILE POLYMERIZATION PRODUCT BEING DISSOLVED IN A CONCENTRATED AQUEOUS SOLUTION OF THE SAME WATER-SOLUBLE THIOCYANATE WHICH IS A COMPONENT OF THE SAID LIQUID COAGULATING BATH. 